Rectifier



C. G. SMITH RECTIFIER Oct. 15, 1929.,

Filed Jan. 22, 1927 lll llllatented llllrtl "l5, M2@

ljlllll SAGHUSETTS, ASSTGNOR TO RAYTHEON WC.,

litEllTl'l'llER application tied January itil, 192'?. llerlul lla. ldai..

elements, it has been proposed to utilize' the vapor of certain alkaline substances introduced into the envelope either by distillation, in which case the electrodes or the inner surface or both of envelope acquire a relatively thick coat of the material or by providing solid electrodes of the material. However, not only has diculty attended the introduction ofmaterial, but in operation, rectiliers containing a certain class' of substance calculated to reduce internal losses have shown marked inferiorityfor one of 'several reasons. ln the matter of distillation the process is quite tedious, expensive and prohibitory in the manufacture of rectiiers on a large scale. Furthermore, the presence of an alkali coat derived by distillation and forming in appreciable thickness on elements in the tube other than the active electrodes, is not conducive to consistent results and may expose lsome of the inactive ele-1l ments to attack by the material. The art, in turning for a solution of the problem to solid alkali electrodes, found that when subjected to electron impact, they disintegrate lill rapidly particularly whenv surounded by gas. blow, l propose a rectifier containinga lilamentary cathode and in vwhich. the bene-l nts of alkali metal are secured in substan-v tial degree without thepdisadvantages noted above. Briefly, this is accomplished by im mersing the cathode in an alkali vapor, the

volume of which is substantially defined;

preferably, the vaporfis confined within the other electrode. By constraining the fluid to a given region removed from the 4leading-in conductors and the glass envelope and other .insulating elements, the deleterious effects A still further object is to provide for the purposes stated, the practical utilization of alkali metals in general. Other objects and features will be apparent upon perusal of the following description when considered in view of the accompanying drawing in which,

'lhe figure represents a preferred embodiment of the invention.

ln the ligure, numeral l indicates the usual glass envelope containing cathode 2 and anode 3, each being of a suitable refractory material. The cathode comprises `a lamentary member depending from rigid conductors d, the latter' being supported by the press. The anode or plate member 3 is similarly held in position by a conductor 5 fused in the glass envelope. It will be noted that the anode takes the general form of a cylinder totally closed at both ends, except for a small opening of sufficient dimension for the cathode leads. lt is apparent that my invention is not limited to a particular shape of anode, the essential point beingthat it is practically or substan tially totally enclosed. During manufacture, the thermionic device is held upright with 'the press in the lower position as shown, and prior to assembly of electrodes, a piece of metallic lithium 8 is placed on the horizontal member of the anode. 'lhe filament is then positioned within the anode and the tube evacuated in the usual manner. When the cathode is enerm gized and potential applied between electrodes, electrons traveling to the plate heat the same until an appreciable vapor pressure of lithium is `built up within the metallic chamber, whereupon the voltage drop falls' off and heating diminishes. rll`his decrease in voltage continues until a value is reached such that the losses in the tube remain practically constant. llovv it appears that lithium melts at 186 C. approximately; boils at M000 approximately; and has a specic gravity of about .5. 'lhe low melting point, combined with the relatively high surface tension of this substance when molten, offers an extreme dll dll

advantage in readily providing a liquid dlm f that spreads evenly over the inner surface of the heated anode. lhis coat presents asur face'which is particularly useful in facilitating clean-up of the various gases without the necessity of excessive heating. The high volatilization temperature of lithium not only minimizes the possibility of arclng on reversed potential but also prevents excessive distillation of the alkali substance from the active portion of the tube. The enclosed anode serves to confine the body of vapor to a region closely associated with a filament, thus preventing its general dissemination throughout the envelope where it may atleet elements external to the anode and cause local discharges or wandering of the arc and other irregularities. Furthermore, by providing a screen between the envelope and incandescent cathode, photo-electric effects and other electrical phenomena resulting from the presence of a small lithium deposit which may have escaped through the aperture in vaporous form andcondensed on the envelope, are prevented. However, ordinarily all Vapor will be chiefly confined to the space within the hollow anode.

are also reduced in substantial degree.

From the foregoing it will be understood that rectification proceeds in the usual manner but the space between anode and cathode .is permeated with alkali vapor resulting in a relatively low impedance between electrodes; the internal losses of the unilateral conductcr t will be apparent that in the final rectifier any of the usual gases may be admittedto the envelope. If desired, the rectifier may be provided with a base 6 of suitable design and plugs 7 to make ready contact with external circuits.

I claim: 1. A rectifier comprisingl an evacuated envelope, electrodes therein, one electrode adapted to emit electrons, another electrode to functlon as an anode and substantially totally enclosing the rst named electrode, and a quantity of lithium, substantially all of which l is within the anode.

2. A rectiier comprising ancvacuated nvelope, electrodes therein, one electrode adapted to emit electrons, another electrode to function as an anode and almost totally enclosing the first named electrode, and a quantity of solid alkali metal inserted within the anode. Signed by me at Cambridge, Massachusetts, this 10th day of January, 1927.

' CHARLES Gr. SMTH. 

